This invention relates to a coupling suitable for a torque-driving connection between elements such as a tool driver head and a driver head of a fastener such as a bolt or screw.
Many fastener head and tool coupling arrangements are known in the art. Common examples of such arrangements are a straight-slotted screw head and ordinary screwdriver, a Phillips-head screw and driver, and a hex-head bolt or screw and driver. However, each of these common types of driver head and tool configurations exhibit certain disadvantages in given applications. For example, in many applications a considerable amount of torque must be transmitted from the drive tool to the fastener to guarantee a relatively vibration resistant and permanent coupling of workpieces or the like by the fastener. Moreover, it is often desirable to provide a relatively tamperproof fastener, such that only a specially configured tool may be used to remove the fastener and hence prohibit tampering or unauthorized removal.
With conventional slotted drive heads, there is a marked tendency to cam out or otherwise destroy or deform the head, primarily due to the relatively insecure coupling between the drive tool and the driver head of the fastener. Such damage becomes increasingly likely as the torque applied by the tool increases. Moreover, many different tools or other objects may readily be fitted in the conventional slotted type of driver head. Hence, this type of driver head is not particularly suitable for high torque and/or tamperproof applications. The conventional Phillips arrangement offers some improvement. However, Phillips-type drive tools in various sizes are widely available, and the mismatching of size between driving tool and driver head can result in similar camming out or damage to the driver head in high torque applications. Moreover, the generally wide distribution and availability of Phillips-type drive tools makes the Phillips arrangement relatively unsuitable for tamperproof applications.
Additionally, slotted or otherwise recessed driver head configurations may be unsuitable in applications where foreign material, including corrosive liquids or the like are present. In such applications, these liquids or other materials may collect in the recessed-type of driver heads, causing deformation or other damage. As a result, the fasteners may become non-removable, or in some cases non-functional in achieving the desired fastening application.
In the conventional hexagonal configuration, the relatively large driving angle and point contacts between the engaged surfaces of the driver head and tool results in inefficient torque transmission therebetween. Moreover, some amount of tolerance is usually provided between the driver tool and the drive head whereby the units tend to be wedged apart and the stress risers or corners of the driven unit can be overstressed and deformed. These problems are overcome to a degree by enlarging the driver head and drive tools utilized, however, the coupling parts then tend to become relatively heavy and expensive. Moreover, conventional hexagonal driver tools are rather widely distributed, and additionally, conventional wrenches, pliers or the like may be also readily engaged with the drive surfaces of a conventional hexagonal head fastener. Hence, such fasteners are not particularly suitable for tamperproof applications.
Other coupling arrangements have been provided to overcome some of the foregoing problems in high torque and/or tamperproof applications. However, many such arrangements have proven relatively complex and expensive in their design and manufacture.